Can my boyfriend adopt my daughter who has been in her life for 8 years already while bio dad hasn't seen her last 4 months with no excuse ??

If you were married, you could terminate the rights of the biological father and do a stepfather adoption without question. However, I have not found any cases that address a boyfriend adoption. However, there is a 2007 opinion from the Attorney General of Tennessee that states:  "Likewise, the joint adoption by two adults who are not a couple and are not cohabitating in the same home is also not contemplated by Tennessee adoption statutes. As noted above, the purpose of the adoption statutes is to place children in a safe, stable and permanent home. Tenn. Code Ann. § 36-1-101. This objective is not likely to be served by allowing the adoption of a child by two adults who are not a couple and not cohabitating. If the court grants a joint petition to adopt by applicants who do not share the same home, the court's next task would presumably be to decide with whom the child would live. That is, it would have to make a custody determination separate from the decree of adoption itself. The adoption statutes, however, do not contemplate custody determinations. Rather, the adoption statutes presume the adoption by two persons will result in the child being placed in a unified and stable household."   The AG opinion uses the term "couple" and doesn't say "spouses" so being married doesn't appear to be required. If you can prove that you are a "couple"  of long standing time period, can establish that the child will live in "unified and stable household", and that it is in the best interest of the child for the adoption, the judge might well approve it.