Talk parents dating
Maybe you're too thin (usually in comparison to their favorite ex-daughter-in-law), or maybe you're too "something" (insert imperfection here).
In any case, you take it with a grain of salt and wear it proudly.
For all you know, this is a test to see if you can handle criticism.
If you're "too skinny" for his mom, you casually respond with a positive tone that you eat very healthy and you're just not gaining anything.
On the other hand, however, maybe you're not ready to commit your face to their memory.
Of course he makes you feel better than anything and he's definitely into you, but this is a huge leap into the very thread of his life.
After all, you just endured a three-hour dinner with your SO's parents, and I'm pretty sure this encounter has either inspired you to keep the love going or take it down a notch.