In the forest, when Seetaa scolded Him for not rescuing Raam even if He called Lakshman for help, She blamed Him for conspiracy with Bharat that He wanted to take Seetaa after Raam is killed. Lakshman thought proper to leave the place immediately but He could not have left Her unguarded in spite of hearing such a great blame. He prayed the Devtaa of forests and mountains to guard Her, drew a line around Her hut and requested Her not to cross that line until they came back.

My Note
Traditionally daughters and daughters-in-law in Hindu families do not cross the limit of their family traditions. So it was that limit which Lakshman reminded Her not to cross it until the men were around in the house. But Seetaa crossed that limit and She had to bear the result of that. For the same reason these traditions which are followed in day to day lives are also called Lakshman Rekhaa and it is believed that breaking those traditions brings some kind of misfortune on the girl and the family.

This episode is also not mentioned in Maanas

Tulasee's Maanas says - When Lakshman and Meghnaad were fighting, Meghnaad guessed that his end is near, so he used Veerghaatinee power on Lakshman. It made Him unconscious. Meghnaad became fearless and went close to Him. He thought that Lakshman had died, so in pride he wanted to take His body to Lankaa, that he had killed Him. He asked his army to lift His body and take it to Lankaa. Now hundreds of warriors were trying to lift Lakshman's body but were unable to even shake it. Seeing this Meghnaad came himself and tried to lift Him. But he also couldn't even shake Him. At this moment Tulasee says it very nicely - "Who is the bearer of the whole Prithvi, how can anybody lift that Shesh Jee." So he shamefully went back. Then came Hanumaan Jee, lifted Him like a flower and took Him to Raam.

Later, when Meghnaad was doing his Yagya for being immortal, Lakshman killed him.

Lakshman got very upset when Raam asked Seetaa to appear in a fire test. He asked Raam several times as "Why Seetaa should appear for the fire test when we know that She is pure." Then Raam said - "But other people would not know it, so this test is not for us but for others." Although Lakshman's conscious still didn't allow this but He could not disobey Raam. He Himself had to make a pyre for Her.

My Note
Tulasee's Maanas is more considerate in this matter. Tulasee's Raam didn't allow anybody else to touch His Seetaa, so He was using a shadow Seetaa after the appearance of Shoorpankhaa. He gave His Seetaa to Agni Dev to be kept safely until He needed Her. Since He did all this secretly, even Lakshman didn't know about this. So in reality, it was not the fire test but a way of getting His own Seetaa back from Agni Dev. How could Raam accept a woman who had lived in somebody else's house for one year? And how could Raavan touch Raam's Seetaa? And how could Seetaa allow anybody else to touch Herself other than Her husband? So Tulasee's logic seems logical.

Although this episode is not mentioned in Raamaayan.

This story is also from Raamaayan, not from Maanas. When the time came for Lakshman to go back to His Lok, Kaal comes to Raam in Tapaswee guise and said to Lakshman - "Atibal Muni has sent me to see Raam for some necessary work." Lakshman informed Raam about the Tapaswee, and Raam asked Lakshman to bring him inside. Then Raam asked the message of Atibal Muni. Tapaswee said - "He has asked me to give you this message in a lonely place, and if anybody will see us or listen to us even secretly, you promise, that you will kill him."

Hearing this Raam asked Lakshman to move the gatekeeper from there and guard them Himself. But when they were talking, Lakshman's Kaal came in the form of Durvaasaa Muni. He came and said - "I want to see Raam immediately. Lakshman said - "Bhagvan, He is busy talking to someone, please wait for a while. As soon as He will finish His talking I will take you to Him."

Muni said - "Don't make me furious, take me to Raam immediately otherwise I will give Shaap to everybody, you, your kingdom, Bharat, your children.." Lakshman thought "It is better to die only myself than to have a Shaap for everybody." So He went inside where that Tapaswee was talking to Raam and informed Him about Durvaasaa Muni. He came out after informing Him.

Lakshman knew that He had broken the promise, so He had to die. He requested Raam to kill Him. Then Vashishth Jee advised Raam that He should leave Lakshman. For a noble man, leaving is as good as his death. So Raam said to Lakshman with a very heavy heart - "Lakshman, To keep my Dharm I leave you." Lakshman started crying hearing this. He came out and went towards Sarayoo River. He didn't even go to His palace There He sat down and by controlling His Indriyaan, he stopped breathing. Indra took His body to Swarg.