Someone who envy's or is jealous of your situation either for a long period of time or short period of time and tries their best to zero in on your spouse/partner and take them away from you regardless if you have a family and/or have a child with the person. The person will do their very best to fill your shoes and have your partner move in with them. It may even go as far as the person eventually marrying your partner and have them neglect the children you have in common!
eg insecure, jealous, envious, betrayal, insensative
Carlos dated his high school sweetheart which he had known since they were 9 years old, Jen noticed they had a great relationship and her family was very pleasant to them, she decided she wanted to share the same special feelings as Carlos and his high school sweetheart,she envied how wonderful her family treated them. Eventually Carlos began a family with his high school sweetheart, to Jen's dismay she told Carlos' sweetie that she liked him and will wait for him. Using her bother as an accomplice he lured Carlos to neglect his family which led him to eventually abandoning them, then Jen began dating and moved in with Carlos. Jen becomes angry with the bond Carlos and his high school sweetie have and tries to manipulate carlos from seeing his child as much as he would like. Jen is a homewrecker.