I can't get my husband to finish!!! Cum holy grail

My husband and I are in our early 30's and we have been trying to conceive. We have always had a good sex life but it wasn't the center of our relationship. Lately he hasn't been finishing. It's very frustrating on my end because I have tried everything to help him get there. It's causing us to fight more and I've become a bit resentful. He chalks it up as nerves and feeling pressured. He says he wants a child with me and he loves me. He suggested ordering some supplements to help increase sperm and fluid so he feels like he has to pop. Anyone ever try anything like that with their husbands/partners? Any other ideas on how to get their partners to finish?