Not a substance addiction but I hope this answer is still contributory. But since mostly anything works as a drug, even the hormones in your brain I will answer this. I'm a love addict. Yes it's a thing and I'm currently on my way to recovery.

So how does it feels like? You become addicted to the feeling of being in love. Mostly you do not realize your are addicted to love. Love addiction can be treated with various recovery techniques, most of which are similar to recovery from other addictions such as sex addiction and alcoholism. I've realised it after my first abusive relationship and I'm trying to fix this issue.

Here's a bit more detail about how I feel. Most love addicts start out attempting to meet some known or unknown emotional need, then become dependent on the intoxicating feelings of being in love itself. Unfortunately, as in the case of drug addicts, "love addicts", too, may become incapable of getting the desired satisfaction, which in turn increases their addiction'. They often feel a burning, passionate love that gives and gives, destroying their sense of humanity when they lose the person they've given to, sometimes causing them to feel and act out in a vengeful way. The love addict suffers a lack of bonding as they did in childhood, including an inability to give and receive affection, self-destructive behavior, problems with control, and lack of healthy long term relationships.

With addiction comes inevitable negative consequences. The consequences of addictive loving are most revealed as the love addict experiences withdrawal symptoms when a relationship ends, or when a relationship is perceived as falling apart. When a break up occurs, an addictive lover longs for the attachment and apparent loving feelings of the lost relationship, as much as a heroin user craves heroin when the drug is no longer available. This longing may result in extreme debilitating pain, obsession, and otherwise avoidable destructive and/or self-destructive behaviors, including violence (to others or self), increased feelings of shame, depression, impaired emotional growth, chronic emptiness, loneliness, and loss of intimacy and enjoyment in life.

I'm currently in a breakup. I suggest my girlfriend of cheating on me. It's going to be a hard time again. So I'm currently trying to recover. It's hard as hell. It's a lot of behaviour-therapy. You just look what you've done wrong and you try to change your perspective on it. Then you work on it until it gets better. You constantly analyse your feelings and thoughts. You seek destructive patterns and try to fix them. And while you're fully aware of your flaws, problems and the things that make you feel bad you still can't turn them off. Have you ever been heartbroken? Multiple this by 10 just when you think about losing someone. The actual suffering is the worst. Three month apathy or more. No will to life. But I'll always try to get back on the track because I know that I'll someday find a loving healthy relationship.