I dont know anymore

My fiancé and I have been going through this endless loop ever since we started trying to conceive where we fight and then we have makeup sex. But lately he's been more distant than usual. Ive caught him sending nudes and sexting other girls before so ive been really paranoid that hes back at it now. When I first found out that he was sexting other girls I wanted to get even so I sent a couple of racy texts to my ex i never sent any nudes but I dont know how he was able to do it and look me in the face because i felt so much guilt and regret. I told him about it when I confronted him and I thought we had worked through it but now hes doing things that I always wanted and he never did. For example, ive wanted a dog since we got our own place 3 years ago and now all of a sudden he's buying me a $1000 puppy and going along with everything that i ask. Im tryong to figure out if its becaise weve been ttc for the last year and a half with no success or if its because hes cheating again. I just dont know what to do anymore, if we talk about not being able to conceive I feel worthless like my body cant do the 1 thing its suppose to and if we talk about him cheating again I still feel worthless but now its because I have to be lacking something for him to want to go fuck with other girls. No matter how I look at it im at fault.