How can I know for sure if I love my girlfriend

Hello Tommy and thank you for asking a question here on BetterHelp. This is a wonderful question! It sounds like you see a lot of wonderful things in your girlfriend and you truly care about her but are still really iffy about whether this relationship is going to last for the long-term or not. But I think the end of your statement shows how you truly feel, you recognize she is way to out of your league. When you said that, your statement no longer sounded like a question about a relationship and instead starts to sound like a self-esteem issue.

But to answer your first question: the best way you can know if you truly love your girlfriend is to be satisfied with who you are as a person first. When we are unsatisfied with ourselves we tend to take it out on our partners or the people that are closest to us, so your insecurity about sexual activity or her being better than you all of a sudden starts feeling like it's the source of your problems. But the reality is that you're not unsatisfied with her, you're unsatisfied with yourself.

Whenever I talk to people about self-esteem, I encourage them to think about it by understanding core beliefs. Core beliefs filter the world around us, they determine how we view ourselves, our relationships, our accomplishments, and all of the people in the rest of the world around us. Think about it like a pair of sunglasses, when you're wearing sunglasses everything you see is filtered through them before they make it to your eyes. A core belief functions in the exact same way. When a core belief is inherently negative, then it stops us from viewing the world in the way that we should. We end up refusing accomplishments or excepting praise from other people, we begin to feel like we are not good enough, we begin to believe that other people feel the same way about us that we feel about ourselves. Common negative core beliefs I hear from people are: I'm unworthy, I'm not good enough, I am ugly, I'm a failure, or I am a bad person. The good thing is we are able to take away the influence a negative core belief has on you, we do that by taking away the power it has over you.  The first thing we have to do is identify what your negative core belief is, take a look at the list I provided and see if one of those stick out for you, it's common for somebody to have multiple negative core beliefs. Once you have identified it, we can start to take away its power. The best way this is done is by you gathering up as much contrary evidence to your negative core belief as possible. This is going to feel very uncomfortable for you at first, you are writing down everything in your life that proves your negative core belief is false. I would encourage you to ask somebody close to you for a little help in this area, as it can be very hard to do this on your own at first. Once you have established this list I want you to continue to add to it daily as well as review it daily. Remember the goal is to prove that your negative core belief isn't true, once again this would feel so odd for you because you have probably convinced yourself over a long period of time that your negative core belief is a fact not a belief. I promise you that this can be changed, and establishing a healthy self-esteem will improve your relationship. But relationships themselves also take some work. 

Whenever I work with couples I encourage them to pursue three things in their relationship, and any long-term relationship needs these three things.

• The first of these is acceptance, you are accepting your partner for who they are and not trying to actively change them all the time or change them into something they are not. Acceptance doesn't mean ignoring bad behavior or pretending bad things in the past didn't happen, instead it means turning off your inner critic and accepting your partner for who they are.
• The next thing we need is gratitude, I have seen gratitude in relationships change marriages. Gratitude is the general thankfulness and appreciation for your partner and the good qualities and things that you're bringing into the relationship. Gratitude is the antidote to resentment and bitterness, it also helps in accepting your partner. When you are actively practicing gratitude you are looking for good things in your partner, this causes you to recognize wonderful things about them you didn't even know before. It also helps you enjoy your partner, we have to talk about relationships and how much work it takes but realistically relationships are supposed to be a lot of fun too.  I want you to have a ton of fun with your girlfriend!
• The last thing every relationship needs is forgiveness, nobody will hurt you in your life as much as your partner and you will never hurt anybody in your life as much as you hurt your long-term partner. We have to be willing to forgive each other  in order for a relationship to work. Think of forgiveness as choosing to not view your partner through the lens of their mistakes. 

I hope you are able to improve your self-esteem and enjoy your girlfriend for who she is.

I also hope you're able to find something in here that helps and I wish you the best of luck!