I have had bad experiences related to relationships in the past, and even now, this is one of the major reasons for my insecurity about many things. I am learning to overcome this by reading, meditation, exercise, and listening.
I mentioned listening, this is an important aspect and helps a lot in overcoming stress and overthinking, being insecure also occurs due to overthinking negatively. I have been practising to think practically and with the facts to be clear about what is true and what is my thinking.
Never try or compare yourself with anyone else as the journey for everyone is different and undefined, and when you compare your life or try to compete with someone unnecessarily it makes you feel insecure and gives you anxiety, even you get distracted easily with all these useless activities.
Rather than comparing myself to others, I follow my own goals and try to work on them regularly to be focused towards self-growth.
One important thing I have observed if our purpose is clear and we know where we are going it becomes a lot easier to ace goals and achieve them by putting in less effort.
I hope this helps, Be focused on self-growth rather than others' imaginations.
If you have any suggestions let me know...