Extreme highs and lows, when it's great, you feel there's nothing that could stop you. You find joy in every little thing, you feel grateful for your existence, despite having a bad day, you get through it perfectly okay and happy coz you have that someone.
When it's bad, it's terrible lol. Anything that remotely reminds you of that person or triggers an unwanted memory could send you into a spiral.
But I'll say everyone needs to experience it once, despite the potential heartbreak and sadness. When you're in love and it's good, it's a special kind of feeling that can't really be duplicated by anything else. Even with the risks, it's worth it.
Past the honeymoon phase, it's a lot of effort and commitment tho, not everyone is ready for it. Sometimes you learn as you go along, sometimes you regret ever stepping into a relationship after finding out you were not prepared at all.