At one time there was a pattern in my life regarding relationships which I hope I have outgrown now, because as far as I am concerned it was not a particularly healthy pattern. I have a natal Venus square Neptune and tended to pick up the Saturns of various partners or 'friends' who often wanted to be more than 'just friends.' whose Saturns were making either conjunctions, oppositions or squares to this aspect. It is what someone once called my 'lame duck' attrractor, as these people often had problems that made them either very clingy or possessive. They did have a way of making feel responsible for this conundrum and that I was being heartless or selfish for not understanding their love or their need.
The last time this happened was in the case of an artist whose company I still miss in other ways because as an artist, he was very much on a wavelength. However, he was also telling me things like I was lucky to have found him because soon I would be too old to get anyone else and that my style of dress made me look ugly. At first, I just thought that this was just cultural differences, but in the end his comments about being ugly did start to get to me a little.
Well, I suppose in this case it has to be a question of 'never mind the synastry' - I would put a stop to tactics like that hopefully right in the bud now, as well as severing anyone out of my life from the start if I liked them only as a friend, but suspected that they might want more than that.
In my family, by brother has his Saturn in my Venus and so does my mother, it is fairly close to my Moon too. There was a lot of emphasis on 'not being selfish' when I was growing up and at school, too much on good Christian values of a Patient Griselda stripe, Sacrifice in Love and all that.
There are other friends and parters where there are other pretty meaty synatreis to say the least, but they have endured. Some Saturn links can be easier to deal with than others I think because they are more easily externalised and in fact, a synastry with no Saturn links is sometimes reckoned not to have the staying power.
To Pluto I would also add Neptune to aspects in synastries that might be problematical, because of the misunderstandings that can develop in its wake. However, there are many relationships other than marriages or lovers which might need to be considered in this context.