Im having issues

Me and my partner been together for five years and we have a one year old and a son on the way, he goes to work everyday with he's father they work st the same place, I know he's there and not anywhere else because he's dad and him talk alot about there work and he also gets paid every week. But for some reason we been drifting apart I don't know If its my hormones speaking but I feel like he's seeing someone else, he been acting weird and taking he's phone to bed usually leaves it with me for he's internet. I might be over thinking things as where going through a lot ATM but he doesn't even cuddle or show me efficient. We had sex last night for the first time in a month and I was into it and showing him love and there was not much coming from he's end :( I texted him this morning talking bout it and he said stop worrying bout it all, I don't know what else to do, I feel ugly and have low self esteem about a lot as I've let my self go, I don't know what to do :(