I wouldn't say the it is a red flag, I would be old fashioned and say that maybe they haven't found the right person. But there are many reasons why this could happen: maybe they have commitment issues, maybe when they hit a certain length of time with a person they get afraid, maybe they just don't want to spend that length with a person; they might like their freedom. You should give it a go. Forget about their track record and give them a chance.
Selective mutism is basically social anxiety. After you get past the first few stages of meeting someone, in any relationship, they open up to you fully. Same with someone with selective mutism. So being in a relationship with someone like that isn't hard after you get past their shell! They will only be like that with others, therefore, nothing from there should affect you being in a relationship with them.
A bad relationship.
Well what I think is if you have a relationship with someone that that person is the only person you like and have feelings for. But if you do have a crush on someone dont act on it, or talk to the person you are in a relationship and tell him/her what you are feeling and see what they say...But its best to forget about the crush because you are in a relationship. But if you dont want to be in the relationship you are in then break up with the person in a kind way and then go for your crush, but to tell you the truth I would stay with the person your in the relationship with because the person you have a crush on might not like you back and then you lose the person you were dating and the person you liked, so you could basically lose both of them.
Someone who suffers from selective Mutism, like Rajesh Kutrapalli in the Big Bang Theory
simply tell the person you are in a relationship with that you are intrested in someone else and just be honest with them and tell them how you really feel.
A relationship with someone who is 'really not into you'. You may also call it a one sided relationship, which is not really a relationship at all.
Well, you have to break up with the person you are going out with. Then you have to wait for the other person to get out of their relationship before asking them out. Don't try to sabotage their relationship. After all, you wouldn't want someone to do that to you. Think about the consequences of your actions before doing anything too drastic.
someone who cares about the other person and cares about the relationship altogether.
Flame
someone also obsessed with that person.
End the relationship just like every other relationship
it depends , if its your relationship, breakup with the person . if its someone eles , leave it alone and let them figure it out