This is a sensitive topic, so please be gentle. What do I do?

I (F24) have been with my partner (M25) for 5 years and he has a younger brother (M14) that is quite shy. We’ve never really been close, just friendly. I got drunk recently and told him that I want to be closer with him because I love him and his brother (my partner), so I plan to be in the family for a long time.

After that night, he messaged me to have a chat and play a game. He told me he wanted to use my makeup and hair products - which I was absolutely fine with. But, he didn’t want me to tell anyone; and I didn’t. We had a great time, getting to know each other, while I did his makeup, painted his nails, and styled his hair.

This weekend, he asked if we could do it again. I said yes. He asked for me to bring my clothes and shoes and a wig that he could use. Again, I was fine with doing this. The part that I want some advice on is that he asked me if I had a pregnant belly or a pregnant simulator I could bring over next time. I just don’t know what to think and I don’t know what to do. Do I ask him? Shall I tell my partner? Help!