People in relationships frequently spend all of their time together, particularly during the honeymoon period. Spending too much time with one person, though, can become harmful and can result in codependency. Therefore, it’s crucial that you maintain a life outside of your relationship and keep some things to yourself.
Any relationship, no matter how healthy, suffers when codependence sets in because those involved lose their capacity for independence (which is difficult and painful to relearn). Even if you’re as certain as you possibly can be that this is the person you want to spend the rest of your life with, that doesn’t mean they can offer the emotional stability, intellectual stimulation, and practical assistance of a whole social circle, and it’s not a good idea to ask them to do so in any case. Friends can provide a completely new perspective on you in a different setting, and those facets of you are just as valuable as your romantic self.
Leaning on one individual for all of your emotional and practical support needs is neither realistic nor healthy. Long-term relationships must eventually face challenging or painful situations together since life is long, things change, and awful things occur. If you have other people nearby who you can talk to and ask for assistance from, people who will listen to you, make you tea or coffee, transport you to hospital visits, and let you scream and whine, it will be lot easier to avoid becoming overwhelmed and to get through when that happens.
You will always also need to take time to yourself and enjoy time alone in order to recharge and be the best partner you can be in the relationship. A life outside your romantic relationship does not mean you love your partner any less, it means you prioritize taking care of yourself, for you and for the betterment of the relationship. You had a life before meeting this person, they should be an extension of your life, not what your entire life revolves around.
Also see: Getting comfortable communicating your sexual desires with your partner