Can moving in together to soon drastically affect a relationship?

Thank you for reaching out and asking this question! It takes a lot to gather up the courage to ask something of this nature and get some additional insight. 

Relationships are complex in nature. They have multiple layers. One important aspect of relationship building is establishing a solid foundation. The amount of time that takes can vary from relationship to relationship. Sometimes it takes weeks, months, or years. In my professional opinion, a solid foundation takes a few things. Those things being respect, established boundaries, and mutual love/affection/feelings for each other. All that plus a general understanding of who each other is. Their likes, dislikes, quirks, and so on.

Now the question of moving in too early or not. Your situation appears to have additional variables, being your three amazing children! It is absolutely different when you are including them in the situation. I have seen situations like this work beautifully and some that have ended in catastrophe. Mostly because of two things, a lack of communication and a break in expectations. In this situation, it appears that your partner did not understand nor expect how that dynamics of the relationship will change and that you all did not communicate what the expectations were when you moved in with each other. This does not mean that this is doomed to fail! You both have started off well by starting to speak about it and discuss how your relationship is different now. This is important and the communication needs to continue in a positive form. Keep this up and really discuss which way you would like the relationship to go. What are you wants, needs, and desires in the relationship. Discuss what you both feel is missing and discuss strategies to address those missing parts. The layer of children is a difficult and complex one because you are also dealing with the feelings of those little ones also. 

Additionally, right now he sees you in "mom mode" most of the time. So find time to show each other the romantic side. Plan little dates inside and outside of the home. Yes, a mother is an important title and an important role you play right now. But it is very easy to get lost in motherhood and forget the other areas of your life. It is okay to want to improve your relationship!

Also discussing the feelings of being taken for granted, ensure that boundaries are in place in your relationship. Going back to discussing those wants, needs, and desires. Also discuss those "absolute no's." Meaning the things you are comfortable with and things you aren't. Discuss the ways you want to be appreciated and the ways that make you feel unappreciated. Also allow him to have that space to do the same. With these communication topics, it is likely that there will be improvement in the relationship. 

I would suggest continuing with individual therapy services so some of these skills can be discussed more and processed together with a therapist! Additionally you will be able to get more tailored suggestions to your situation. I truly hope those helps and good luck with your relationship!