My take on this and answering a few comments/points made:
1. Lillie met Gary Beadle from Geordie Shore away from the TV cameras and they were together for a year. They were really happy until Gary decided he wasn't feeling the same way. Their split was in the media because at the same time Gary decided he wanted to give things a go with his on/off co-star Charlotte. Lillie kept a dignified silence on this for a long time and even now, I've only seen a handful of comments and they are following her being trollied and bullied by GS fans. The press has twisted a lot of words and so it looks like Gary, Charlotte and Lillie are all at war.
2. Lillie met Bear on Ex on the Beach, which she is to confront Gary. The series has just started so it is unclear what happens in both of those relationships but it looks like Gary cries when speaking to her. We don't know Lillie's side so far, just what we see in the media.
3. Lillie has her own fashion line and fair enough she has built up a profile from being linked to reality stars and now being on a reality show, she seems to be happy in her career and is already wealthy so isn't out for fame or fortune in my eyes.
4. What happened with Gary must have been sad and upsetting for her as she had to deal with a break up and immediately afterwards seeing her ex get with someone else on a TV show and face it daily in the press and on her social media pages - goading her into a reaction. Now she has had this happen which has been live on TV when she was still with the guy, it just makes her feel humiliated and again she has to deal with the social media in her face daily so she can't hide from it.
5. I think she went into CBB to do what she said, face her ex boyfriend by looking him in the eyes and explaining to him, the housemates and public that he was not the person she knew and his behaviour was shocking to her and had humilated her. This statement made me think that this will explain to people why she is with him and why she did not expect him to cheat (a lot of people are saying he is a player and only knew her 2 months and it couldn't be serious etc etc). I think Bear's reaction made it clear that he has been putting on an act and whilst he probably does regret hurting her, he is just in there playing a game and not taking it seriously - her appearance made him realise life on the outside still goes on