I have two answers, for two different aspects of this question.
First, I say no.
I feel as though social networks don't ruin the relationships, people do. Plenty of times a relationship can get ruined because of their partner feeding into the things that go on while they are on the social network (i.e Facebook Chat, Twitter DM's) I feel as though if that person that is in the relationship acted as if they were still in the relationship on social networks, then it wouldn't be any problems. People use social networks for the wrong reasons now a days, trying to jump down on females, or having a chat buddy when their bored late night, & thats what causes the problems.
I dated a guy in the past & everything was cool until I got a hold of his Myspace (this was a minute ago lol) & I found out he was living a double life. I mean he was basically in relationships with other females that lived in different states. I was stunned as I read through all his messages; but not for once did I blame Tom or Myspace. I blamed my ex, because that was his actions that made me lose the trust & end up breaking up with him.
A lot of people feel as though when they are on Facebook or Twitter, they can be a different person. They forget who they really are, forget they have a relationship & think that no one is really watching. They flirt & feed into everything that they shouldn't feed into. So to sum up my answer, No, on this scale, social networks are not to blame, the person actually acting on those things is to blame.
Reason why I am saying yes now is because I feel like social networks can ruin relationships on this aspect because their is no "real relationships" anymore. So many people are stuck on their phones 24/7 that while they are with their significant other they rarely talk. I know we are in a technology savvy world now & thats cool, but when it comes down to really whats important in life, why are we not making time for it?
Every time I come to visit my mom she has to ask me to put my phone away, & when Im with my significant other we BOTH have glued faces to our phones. I just realized recently how much I am actually on my phone. I am on Twitter almost all day, I check my Facebook about twice a day & not to mention the other reasons I'm on my phone, like blogging & checking up on gossip.
All I'm saying is that when you are with your family, friends, or significant other try & check all your notifications after you leave their presence. Next time try this, put your phone away & see how much of a difference it is when you are with them. See how much more yall talk, or laugh. I did it last weekend & I was shocked. I could really see the difference when I left my phone in my bag.
...A social network can get in between a relationship in this aspect, but why would you let it?
