I am not an ML and no one I ever dated was an ML at the time. So i answer relative to myself.

In general I much prefer to date people with closely aligned politics. Or even better, someone who is more developed in their politics than I am, more ambitious, more serious, more experienced. When I can get it. I eventually find the non-left people boring and annoying for any but the most casual or brief relationships and the feeling is often mutual. I enjoy a diversity of people in my life generally but to date someone you end up spending a lot of time with them. If a person is just not interested in collective improvement for humanity, or worse they are opposed to it, there is a finite amount of time to be shared. That time can be fun while it lasts and if the sex is good or there is some other common interest it can be extended.

OTOH, as someone else mentioned, dating within orgs and close tendencies might not be a good idea. In heterosexual couples it very often ends up that the woman becomes marginalized in a breakup, even when there is not a lot of conflict and no overt patriarchal actions taken. I think men and women who date their comrades should consider managing the end of their relationship from the outset to avoid this. And other comrades around them also need to take responsibility for making sure the woman does not get disposed of this way, because it seems to be a phenomena which is very likely otherwise.

OTOOH, being a revolutionary is extremely sexy in a way which is very appreciated by comrades so some hanky panky is inevitable and can strengthen bonds and trust. Just make sure you arent in some kind if spycops type scenario. Probably best to steer clear of the SWP and such. Who i doubt are MLs anyway.