Why are you always "going". I think you make some very valid points. Though if I may add a bit not only to what you wrote but to what others wrote as well.
Tom was the guy for Betsy, had he lived he would have been the number one guy in her life. Unfortunately he's dead and I highly doubt we will ever see him again.
Therefore Warren has become that guy. I just think the whole relationship makes sense. They both had a similar upbringing, and come from similar backgrounds. They both have been through very traumatic experiences in their lives. While they have dated other people, they ultimately end up back together. Some around here think that their relationship is dysfunctional and that they don't go well together and are using Remender's X-Force as an example. What some overlook is that Remender needed it to be dysfunctional. He needed the relationship to be full of turmoil, he had to have it on a shaky foundation. It was a big part of The Dark Angel Saga. She wasn't with him because she was attracted to the death persona as some claim, she was with him because she cared about him. She was trying to prevent it from taking over Warren. It was her sole reason for being in X-Force. She promised to help him, once she killed him she failed at that. In the Marvel Universe the X-Man relationships are the most dysfunctional of all. While Warren and Elizabeth may have had their problems, they certainly weren't the worst X couple. When the relationship wasn't full of dysfunction I think they were both happy.
As for Elizabeth's current relationship with Fantomex. I don't really like it mainly because it feels so forced. It feels like Rick Remender took his two favorite characters and had them shack up. On top of that it's all built on manipulation and lies. Fantomex used his misdirection to get her to doubt not only herself but her relationship with Warren. Even he himself told her that during the otherworld arc. He was mentally preparing her to kill Warren just in case. When he calls her out on being needed that was just a load of bull. Then when Warren dies you have them pretty much cast him aside with little to no impact on Psylocke and soon thereafter she jumps into bed with Fantomex. He goes after her when she's emotionally vulnerable. She herself admits to not caring about Fantomex afterward yet when he dies she supposedly loves him and wants to avenge him. Where did this come from? You also have the fact that Fanto supposedly is madly in love with Betsy yet he sleeps with Mystique knowingly. He better keep that mask on because if Betsy finds out I think she'll kick him to the curb, that is to say if she hasn't done so all ready in Humphries X-Force.
For now I think Elizabeth should be alone. Let her stand up on her own two feet with no one hindering or assisting her. Show that she can be strong without any guy. Perhaps more importantly have her deal with some unresolved issues on her own.