Your mom wants to show how grateful she is that you stepped up to the plate ever since she got pregnant. When your dad left her she certainly wasn't anticipating on getting pregnant again, but after a one night stand that's the situation she found herself in. She never would have been as comfortable as she has been if it weren't for you. You did let her move in and pay all her bills after all. She's about to start her maternity leave and since she's going to have more time around the house she figured now was the time to say thank you. She knows how lonely you've been ever since you and your girlfriend broke up, and she proposes that maybe she can help you out. She slowly strips off her clothes and reveals her pregnant body. You're trying not to stare but the sight of your moms natural body is getting you so hard. She can tell you like it and she assures you it's okay if you two take care of each other. She pulls out of your dick and wraps her massive swollen tits around it, giving you a tit job until you can't hold back anymore and blow all over her tits. Mommy isn't done yet though, she hasn't cum after all. She gets you hard again by grinding her pussy on your cock and then slips you in and starts riding you, with her big belly bouncing in your face. She cums on your cock while simultaneously begging for you to cum inside her, which you can't hold back and obey. Your cum is leaking out of her pussy and you love knowing you're the one who made a mess in your Mommy.