Complicated Relationship

My boyfriend and I have been together for 10 years. We have children together (a girl and a boy). Lately things between us has been on the rocky side. We are always getting in arguments. We had a really big argument this morning right before going to work. Basically I've mad the decision to go ahead and get my tubes tied. I've always expressed myself on only wanting 2 kids and he's always been ok with it. Now for some reason now he's pushing me to have another one. My surgery day is already picked out for next month a few days after my birthday. Not only has he been trying to convince me to have another child he's also been accusing me of cheating. 
The only reason why I feel like he's accusing me of cheating I because I asked him a very serious question a few weeks back about where is our relationship going. This is not the first time that I have asked him this question and he always found a way to change the subject. I feel like we are a point in our lives where we are just together because of the kids. I honestly don't want to teach my kids that it's ok to be with someone if you no longer love them. The love I have for him has changed. I'm not saying that I don't love him I'm just saying that love him because he is the father of my children. I hope this makes sense.