I see what you're saying here brother, but it can also back fire, it all depends on the person. Most of the time when I'm with girls theres alot of eating (dinner, take out, them cooking meals) and boozing (wine, shots, brews), but on the flip side sex is great cardio so you'll be burning alot of cals, so in the end for me atleast it kind of cancels one another out. However, sex is a great stress reliever, so less cortisol=more fat burning. But I've seen friends of mine literally put on some serious lbs when getting into relationships in really short time span, just cause all the dinners/takeout/dates and shit..