paar27 said:
Recently, we had a phantasy of my woman having sex with one of our neighbours (we live in a condo block). It's a 50 yo guy who has shown clear interest in her, and it wouldn't need much from her side to make it happen. This phantasy is clearly turning her on, and I can see at some point, she will show him her availability. But now, I'm not sure it's a good idea to get one's girlfriend banged by a neighbor.
Your phrase, "not sure it's a good idea to get one's girlfriend banged by a neighbor," implies you are in control of your woman's sexuality and will make the decision whether (or not) she fucks him.
Since your neighbor is ready-at-hand, however, and since he has made it clear he's interested in your woman, and she is interested in him, if you discourage her from fucking him there's a good chance that will provide her with the modest additional incentive she needs to go ahead and do it — most likely when you aren't around. I mean, hey, she could even slip out the door while you're sleeping late at night, then tap on his door and fuck him. This would have the benefit of yielding, for her, an "erotic secret."
Thus, I suggest a discussion with your woman in which you tell her you know she needs sexual satisfaction above and beyond what you can provide, so you're going to leave it up to her. If she wants to fuck your neighbor, she should go ahead and do so. However, you feel it will be best for your relationship if she doesn't try to hide that, but rather tells you about her sexual adventures with him (perhaps while holding your cock in both hands, while you're in bed at night, or your cock in one hand and your balls in the other).
Re. whether it will be "awkward" when you see him, say, in your condo hallway: I wouldn't worry about it. More than likely, he'll continue relating to you in the same way he has previously. If he expresses an interest in talking about enjoying the pleasures of your woman fucking him, you can point out that she's her own woman. She dates, seduces, and fucks whomever she wishes, while you don't feel a need for that so you remain faithful to her (if that's the nature of your relationship). An explanation along those lines would be fairly short and simple.