Are you saying that there are women without issues outside his circles? Maybe there is someone somewhere without any issues but the chance to find that person is absurdly tiny.
Well it's not just them having issues that's the problem. It's that those issues have been prohibitive to a relationship, either specifically with Marten or with anybody in general.
Dora is very insecure due to her childhood, and while with Marten her insecurities about his "near-miss" with Faye is what ultimately caused them to break up. And speaking of Faye, she couldn't date anybody for a long while because of her father killing himself. She has a very big problem with fear of abandonment, and that's what kept her from dating Marten even when she thought that she wanted to. She's with Angus now, and they have fantastic chemistry largely because he's provided a strong "Secure Base" that addresses Faye's fear of being abandoned. If he moves away to the big city, it might become a problem yet again.
Hannelore is so afraid of physical contact that a relationship for her at all is still pretty much out of the question, although it seems she has been making some very slow progress on that front.
Claire is trans, and we haven't really gotten an idea about how she wants to handle her romantic life. But regardless of that, when I see Marten and Claire interact they just seem so much like brother and sister to me. Anything could happen, sure, but right now I'm not really seeing those two as a couple.
So yeah. Maybe "issues" is not the right word. Maybe incompatibility is what keeps him from being with any of his current lady friends (in my mind). And yes, I know that most people have some sort of "issues". I wasn't trying to imply otherwise, although I do think it's any given individual's responsibility to bring the issues down enough that they can maintain a romantic relationship, if it's something that they desire (such as Faye and Dora did with counseling).
Marten stands nothing to lose and a lot to gain by seeking romantic partnership outside of his current immediate circle. One benefit to meeting women outside of school/work/friend circles is you get to explore far, far more options than you have if you only date inside of those circles. You also have no worries about dating a certain person being "unethical" because you work with them or something.
The biggest benefit I see for him is taking some initiative, which seems to have been his biggest problem since the comic started - a lack of real direction or drive. He doesn't need to become a full blown PUA, but right now (as has been said on the forums countless times), he's doing a ton of things for everybody else but nothing much for himself.